Auditing User administrator

Background:
I a trying to audit user administration on a AIX box. I am trying to make sure that any changes made by the System administrator to the user accounts (Add users, changing their attributes or deleting users) are accompanied by authorization i.e. the system admin does not make any changes w/o a written authorization.

Problem:

I need to generate a log report that can capture all changes made to user accounts (Addition of users, chanegs or deletions) from the past couple of months so that I can select a sample from that report and ask him to provide me with authorizations. How do I generate such a log report.Also, Auditing might not have been turned on.